Electroconductive paste compositions have hitherto been used in the field of electronics for various applications such as IC circuits, electroconductive adhesives, and electromagnetic wave shields. In particular, the following production process of a printed wiring board has recently been proposed. In the production process, a first board having conical electroconductive bumps, formed using an electroconductive paste, at predetermined positions of its at least one side is provided. Further, a second board having a wiring pattern on its at least one side is provided. The first and second boards are placed so that the electroconductive bump side of the first board inwardly faces the wiring pattern side of the second board. An insulator layer is disposed between the first and second boards to constitute a laminate assembly. The assembly is then lamination pressed to allow the bumps to pass through the insulator layer in its thicknesswise direction to form an electroconductive wiring part (Japanese Patent Laid-Open No. 350258/1994).
Further, a proposal has been made on an electroconductive paste composition for interlayer connection in a printed wiring board, comprising a melamine resin, a phenolic resin, an epoxy resin, an electroconductive powder, and a solvent, the epoxy resin having a softening point of 80° C. or above and 130° C. or below (Japanese Patent Laid-Open No. 270033/2002). The claimed advantage of the electroconductive paste composition is to provide an electroconductive paste that can prepare bumps having good prepreg penetration, does not cause cracking and breaking upon the penetration and pressing, and can realize large adhesive strength between the bump and a wiring pattern after the penetration, and, in the manufacture of a printed wiring board comprising a throughhole-type electroconductive wiring part, can realize high yield and good connection reliability.
Further, in order to provide an adhesive paste composition for interlayer connection in a printed wiring board which can form bumps having high hardness and free from cracking and poor connection with a wiring pattern, a proposal has been made on an electroconductive paste composition for interlayer connection in a printed wiring board, characterized by comprising at least a resin, selected from melamine resins, phenolic resins, and epoxy resins, an electroconductive powder, and a dihydric alcohol and/or trihydric alcohol with a boiling point of 180° C. or above (Japanese Patent Laid-Open No. 77337/2003).
An electroconductive resin composition characterized by comprising a water-soluble heat curable resin, electroconductive particles, and a dihydric alcohol is known as an example of a heat curable electroconductive resin composition that does not cause any problem even when an apparatus, a tool and a vessel are washed with water after screen printing (Japanese Patent No. 3588400).
As with Japanese Patent No. 3588400, Japanese Patent Laid-Open No. 286924/1997 discloses an electroconductive resin composition which does not cause any problem even when a screen plate and the like are washed with water after printing. The electroconductive resin composition comprises a water soluble thermoplastic resin, electroconductive particles having an average particle diameter of 0.05 to 50 μm, and a dihydric alcohol.
Japanese Patent Laid-Open No. 11388/2001 discloses an electrode paste composition for a stacked capacitor, which does not cause any problem even when a plate used for printing is washed with water. The electrode paste composition comprises a water soluble resin and glycols.
Japanese Patent Laid-Open No. 331648/2003 and Japanese Patent Laid-Open No. 265826/2004 disclose a metal paste, which can realize firing at a low temperature, comprising an organometal compound of a group 3 to 15 metal of the periodic table and an alcohol compound, preferably glycols.
The formation of electrode bumps by the method as described in Japanese Patent Laid-Open No. 350258/1994 is disadvantageous in that, when the electroconductive paste compositions as disclosed in patent documents Japanese Patent Laid-Open No. 270033/2002 and Japanese Patent Laid-Open No. 77337/2003 are used, bumps having a height large enough to penetrate the insulating layer cannot be formed by single coating work of the electroconductive paste composition and, thus, overprinting by repeating a plurality of times of coating work of the electroconductive paste composition was necessary. In particular, a paste, which forms bumps not having an excessively sharp tip, should be used for avoiding breaking or chipping of the bump during the penetration and pressing of the insulating layer, and, thus, satisfactory bump height could not be provided. Accordingly, in most cases, the number of times of overprinting should be increased.
The techniques described in Japanese Patent No. 3588400, Japanese Patent Laid-Open No. 286924/1997 and Japanese Patent Laid-Open No. 11388/2001 use water soluble resins, and the techniques described in patent documents Japanese Patent Laid-Open No. 331648/2003 and Japanese Patent Laid-Open No. 265826/2004 use firing-type metal pastes. Unlike these techniques, the electroconductive paste composition according to the present invention is of a water insoluble and non-firing-type and can realize satisfactory coating thickness by single coating work. So far as the present inventors know, such electroconductive paste composition has not hitherto been provided.
An object of the present invention is to solve the above problems of the prior art mainly by using a bump forming aid containing a specific compound.